Apple Cider Vinegar is a well known traditional food additive for horses and humans alike. 
 
DETAILS :
Apple cider vinegar is a completely natural product. For centuries people have been using natural apple cider vinegar as both a food and a medicine for themselves and for their pets. Feeding Cider Vinegar can help to stimulate appetite; acidify the stomach; repel flies and other insects such as bot flies, whilst also improving the general health and coat condition of the horse.